(mfont__lookup_fontset): If only a fallback font is found, don't use it for more than one character.
(mfont__lookup_fontset): If only a fallback font is
found, don't use it for more than one character.

xmirror/m17n-lib,xmirror/m17n-lib,xmirror/m17n-lib,xmirror/m17n-lib